The invention relates generally to switches for interrupting the flow of electrical current in electrical circuits and, more particularly, to a new and improved vacuum switches for high-voltage circuits.
Vacuum switches are used in several different applications. A vacuum switch may be used for capacitor switching or for sectionalizing a line or system of switches. A vacuum switch may also be molded into a "load break" elbow connector to interrupt currents of medium voltage distribution systems. A vacuum switch may also be molded into a solid insulator or be used in a switch enclosure under oil. Typically, vacuum switches are employed as a high-voltage vacuum circuit interrupter.
Load break switches used in voltage power distribution range circuits are of four general types. Air break switches which rely on air for installation. Oil insulated switches where oil is both an insulator and an arc quenching medium. Another class of load break switches for distribution systems is gas insulated switches which employ gas for both insulation and interruption. Sulphur hexafluoride, either alone or mixed with other gases such as nitrogen, is used. Such switches can be of the gas-blast or puffer type in which the arc quenching gas is caused to flow across the contacts as the arc is formed.
The fourth class of load break switches employs vacuum interrupters. High-voltage vacuum-type circuit interrupters are well known in the art. As used herein, the term "high-voltage" means a voltage greater than 1,000 volts. In these switches, the contacts are enclosed in an evacuated chamber. The vacuum environment rapidly dissipates the gaseous products of the arc drawn between the contacts of the switch to effect interruption of the current when the switch is opened.
Typically, a vacuum circuit interrupter includes a pair of electrodes, one being stationary and the other movable between an open and closed position to open and close the circuit. Although vacuum circuit interrupters may be used in either a single-phase or three-phase system, they are commonly used in three-phase systems with three or multiples of three switches mounted in a common grounded metal enclosure. The enclosure includes an insulating medium which surrounds each vacuum interrupter. The insulating medium can be air, oil, or sulphur hexafluoride. U.S. Pat. Nos. 3,048,681; 3,048,682; 3,586,801; 3,777,089; and 4,158,911 illustrate vacuum circuit interrupters having opposed electrodes, one being stationary and the other being movable. Such patents also disclose metallic shields to shield portions of the interior of the envelope or housing of the interrupter from the metal on the electrodes which is vaporized upon the creation of the resulting are upon opening a gap between the electrodes to open the interrupter.
U.S. Pat. No. 4,568,804 discloses a high-voltage vacuum type circuit interrupter. The interrupter includes a ceramic insulating housing mounted on a metallic base and lower housing which includes an actuator. A vacuum module having a housing with an evacuated environment is disposed within the ceramic insulating housing and includes a pair of switch contacts. One switch contact is stationary and is electrically connected to a top or switch electrical terminal. The other contact is moveable and is electrically connected to a line terminal and electrical ground. A dielectric operating rod is connected to the moveable switch contact and to the actuator. The switch contacts are mounted within a metallic vapor shield. A metallic bellows is used to seal the lower moveable contact.
Another form of a vacuum switch is shown in U.S. Pat. No. 2,981,813. Two opposed stationary contact rods extend into a hermetically sealed and vacuumized envelope with a gap between the terminal ends thereof. A contact means in the form of a copper disk is mounted on an actuator shaft. The actuator shaft includes a dielectric post having one end affixed to the contact means and the other end affixed to a metallic rod extending through an expansible metallic bellows and through an aperture in the envelope for connection to a operating means for actuating the contact means. The dielectric post electrically insulates the contact means from the rod and bellows. One end of the bellows is hermetically sealed with the envelope and the other end is connected to the inner end portion of the rod. Both of the coaxial main contact rods are stationary.
High-voltage vacuum-type circuit interrupters and the individual components thereof have many varied and generally complex and expensive configurations. Typically, prior art interrupters include an actuator rod which moves one of the current carrying members to open and close the circuit. Thus, the moving electrode includes a current interchange from which it is difficult to dissipate the heat produced by the arcing and opening the circuit. Only the stationary contact tends to dissipate any major amount of heat. Further, in conventional interrupters, there is a great distance between line and ground which must be insulated. Sometimes the actuator rod can be as long as 20 inches for 27 kv voltage. Thus, a large line-to-ground insulation is required.
The present invention overcomes these deficiencies of the prior art.